Heretofore, adhesives using polychloroprene as the base material are mainly of a solvent type. However, in recent years, problems at the time of using or producing solvent type adhesives, such as environment pollution, danger of inflammability, hygiene, etc. due to organic solvents have been pointed out, and the demand for not using a solvent is increasing.
As a method for not using a solvent, a method of substituting a latex adhesive for the solvent type adhesive is considered to be effective, and a study on latex adhesives employing various polymers has been actively carried out.
Among them, a polychloroprene latex adhesive exhibits a high adhesive force immediately after bonding by applying it to both adherends to be bonded, drying such adhesive layers, followed by bonding. From such a characteristic, it is expected to be utilized as an aqueous contact type adhesive. Nevertheless, as compared with a solvent type adhesive, it is inferior in the adhesive performance such as the initial adhesive strength, water resistance, etc., and an improvement in this respect has been desired.
Heretofore, as a technique for emulsion polymerization of chloroprene, a production method has, for example, been proposed wherein a metal salt of disproportionated abietic acid or an alkyl sulfonate compound is used as the main component of the emulsifier, and a nonionic emulsifier such as nonylphenol is used as a sub-component (e.g. JP-A-52-992, JP-A-52-27494, JP-A-51-136773, JP-A-52-91050 and JP-A-7-90031). In such an emulsifying system, it is difficult to produce a polychloroprene latex constantly, and when the produced latex is used for an adhesive, the performance tends to be inadequate. Further, a nonylphenol emulsifier is designated as an endocrine-disrupting chemical and thus is not preferable.
Further, a method for producing a polychloroprene latex adhesive has been proposed which comprises polymerizing chloroprene in the presence of an unsaturated carboxylic acid, a polyvinyl alcohol and a chain transfer agent. However, with such a polychloroprene latex, the adhesion water resistance has been inadequate (e.g. JP-A-06-287360).